Marvel Avengers Assemble could have gone very wrong. With more superheroes amassed in one film than you can wave a hammer at, director Joss Whedon could have had a battle on his hands, with off and on-screen egos punching everything else out of the park. But this, claims its cast, isn’t the Robert Downey Jr show, or anyone else’s for that matter. In fact, it seems ‘assembling’ came naturally.

‘I know it sounds trite but we had a riot,’ says Hollywood’s new favourite Brit, Tom Hiddleston. The chiselled 31-year-old, who reprises his role as Thor baddie Loki in the movie, had a ball hanging out with his fellow Avengers at the home of his character’s arch nemesis. ‘Chris Hemsworth [Thor] had a house with a swimming pool and a table tennis table and we’d all go round there for barbecues. I might have had no picnics on Hampstead Heath last summer but I did have an American Avengers summer camp in New Mexico.’

The Avengers dates back to a 1963 Marvel comic, when the team comprised Iron Man, Thor, The Hulk, Ant-Man and Wasp. The first three feature in the film (Downey Jr is back as Iron Man, Hemsworth is Thor, while Mark Ruffalo takes on Hulk).

Now, of course, there’s also Samuel L Jackson’s Nick Fury, the mastermind who unites them under the banner of his international peacekeeping agency, S.H.I.E.L.D. ‘I’ve got all of them on speed dial on my phone somehow, or Nick does,’ says Jackson, sitting alongside Hiddleston and the rest of the cast the day after the film’s splashy LA premiere. ‘That day on the set when they all showed up was the coolest day ever,’ he adds. Indeed, Jackson is right at home in the world of superheroes. ‘I’m reading Resurrection Man right now,’ he says. ‘When I was a kid, my favourite was The Flash. I never thought I would be able to fly or anything but I figured if I practised hard enough, I could run really fast.’

In blockbuster terms, the $220million Avengers is about as hyped as they come. But for Hiddleston, the scale of the project had its problems. ‘It was the most monumental spectacle,’ he says, ‘so it’s a challenge to dial up the menace to justify the thing that everyone has come to see. I was exhausted because of Loki’s negative energy – having to cultivate that hatefulness every day, get inside his reservoirs of pain and make them real was draining. He’s just a really, really unhappy guy.’ Thank goodness Jeremy Renner, who plays Hawkeye, and who has just wrapped the fourth Bourne movie, has a solution. ‘Loki just needs to get laid,’ he jokes.

Surely though, whatever the trials of magnitude, tearing about in super-cool costumes made up for it? ‘Some of the stuff you learn is so ridiculously fun, it’s like being a kid at the fair,’ agrees Hiddleston. ‘I did a lot of wire work. The child in me was so thrilled, I had to stop myself going: “Wheeeee!”’‘So many impractical suits,’ laughs Renner. ‘Hey, they all look cool and bad-ass but I was happy to learn very quickly that I was a super-marksman thanks to CGI. I only had to train to be quick – hand-to-hand combat and knife training. But I love learning. It’s like a new language or a fun skill set you get to keep.’

Mark Ruffalo was a tad less enamoured of his own gestation from regular 44-year-old family man to screaming green behemoth. ‘The hardest stuff for me was making The Hulk come to life,’ he says.

‘I had to walk around in a motion-capture suit, yelling and doing other physical stuff, and it was embarrassing. Everyone else was beautiful and strapping in their cool clothes and I was in a frumpy suit. Bruce Banner has a brain and is precise. I was worried he was just going to bland out in this group of incredibly cool, compelling charismatic, beautiful people.’ Happily, Hulk also has an ongoing comic device involving his trousers. ‘I was thinking: “Does Bruce have a little Speedo that he wears underneath?”’

Chris Evans chips in, recalling his own transformation nightmares. ‘My mask keeps the heat in, and once it’s on, it’s on.’ He also had an unforgiving fitness regime, with hardly a gap between filming his own Captain America movie and reprising the role for Avengers.

‘I feel like for a full year I’ve just eaten very bland chicken with broccoli,’ he says. ‘When we finished Avengers, there were a lot of doughnuts and ice cream involved.’

Evans, who admits he’s no fan of pumping iron, was daunted by the prospect of bulking up alongside Hemsworth. ‘When you’re working out next to him, well, Jesus, he’s huge,’ he says. ‘The guy just works out forever.’Rumour has it Evans was more keen on being the cast’s social secretary, summoning the ‘troops’ with a one-word text. Is it true? ‘Yeah, I’d just say: “Assemble!”’ he laughs. ‘Hey, I like a drink or two now and then. But Scarlett Johansson could get us going too.’